Radio frequency (RF) receivers are used in a wide variety of applications such as television receivers, cellular telephones, pagers, global positioning system (GPS) receivers, cable modems, cordless phones, satellite radio receivers, and the like. As used herein, a “radio frequency” signal means an electrical signal conveying useful information and having a frequency from about 3 kilohertz (kHz) to thousands of gigahertz (GHz), regardless of the medium through which such signal is conveyed. Thus an RF signal may be transmitted through air, free space, coaxial cable, fiber optic cable, etc. One common type of RF receiver is the so-called superheterodyne receiver. A superheterodyne receiver mixes the desired data-carrying signal with the output of tunable oscillator to produce an output at a fixed intermediate frequency (IF). The fixed IF signal can then be conveniently filtered and converted back down to baseband for further processing. Thus a superheterodyne receiver requires two mixing steps.
For example, a television receiver may translate one channel in the band of 48 megahertz (MHz) to 870 MHz to an intermediate frequency of 44 MHz. And within the United States, FM radios will typically translate FM audio signals, which are broadcast in 200 KHz channels in the frequency band from 88.1 MHz to 107.9 MHz, to an intermediate frequency of 10.7 MHz. Because of the wide frequency range required of television receivers, it has been difficult to design high quality television receivers at low cost.
High quality television receivers have been traditionally formed with discrete components such as inductors, varactors, and capacitors. While the performance of these receivers has been good, they are expensive and bulky. It would be desirable to utilize the cost advantage of modern integrated circuit technologies. Unfortunately, existing silicon-based television tuners do not perform as well as discrete tuners and have not become significant in the marketplace. Moreover, television receivers that do use integrated circuit technology while retaining acceptable performance have still required external, discrete components, adding to their cost. Thus the promise of integrated circuit technology in reducing the cost of television receivers has not been fully realized.
What is needed, then, are new receiver architectures for applications such as television receivers that retain the high performance of discrete receivers but also take advantage of the reduction in cost afforded by integrated circuit technology.